Many industries use both lower purity oxygen and high purity nitrogen in their operations. For example, in glassmaking the oxygen is used in the glass furnaces as part of an oxy-fuel combustion process and the nitrogen is used as an inerting atmosphere. The power costs to generate these products is high. In an attempt to lower the power cost of generating both lower purity oxygen and high purity nitrogen, the conventional double column system for separating air into high purity oxygen and high purity nitrogen has been modified by the addition of a side column driven by feed air condensing in a bottom reboiler. While this system is very effective, additional power cost reduction is desirable.
Accordingly, it is an object of this invention to provide a cryogenic rectification system for producing lower purity oxygen and, optionally, high purity nitrogen, which operates with reduced power requirements over that of heretofore available systems.